How to Size a Portable Air Compressor for DTH Drilling: Pressure, Flow and Site Conditions

1. Define the drilling duty first

Prepare a duty sheet with target hole diameter, depth, orientation, rock, expected fractures or water, elevation, temperature, drilling method and production schedule. List whether air also feeds foam, water injection, dust control or auxiliary tools. Confirm that the rig accepts the selected rod, hammer, bit and air connection, and check rotation, feed, pullback, mast and maximum-pressure limits. A manufacturer brochure is model-level guidance; it does not prove which options remain on one used machine.

• Hole geometry and production target
• Rock, fractures and expected water
• Elevation and temperature range
• Rig limits and simultaneous air consumers

2. Select the exact hammer and chart

Choose bit diameter and shank, then identify the exact hammer model and execution. Nominal size alone is insufficient because designs can have different pressure ranges and air demand. Use the current manufacturer chart to read airflow at the intended working pressure, and record its edition, units and reference conditions. Mincon states that its charts use defined atmospheric conditions and that altitude increases demand, so the plotted value is a starting point rather than a job-site guarantee.

• Exact hammer model and execution
• Bit diameter and shank
• Working-pressure range
• Air demand at the selected pressure

3. Separate pressure from airflow

Pressure and flow are related but not interchangeable. Within the permitted range, pressure supports the pneumatic impact cycle, while air volume operates the hammer and carries cuttings through the annulus. A compressor can advertise high maximum pressure yet deliver too little flow at that pressure. Compare pressure and free-air delivery at the same operating point. For a variable-pressure compressor, use the full curve or table rather than pairing the highest pressure from one row with the highest flow from another.

• Required hammer pressure
• Required airflow at that pressure
• Compressor flow-pressure curve
• No mixing of incompatible headline ratings

4. Account for the complete air path

Air passes through valves, couplings, hose, swivels and drill pipe before reaching the hammer. Restrictions create pressure loss. Atlas Copco's Compressed Air Manual explains how internal diameter, length, flow and fittings affect pressure drop and says flexible hoses and couplings must be included. Hole cleaning also depends on returning air through the annular space and on cuttings, depth and water. There is no responsible universal margin: document the proposed air path and ask the hammer or tool supplier to review it.

• Hose and drill-pipe internal diameter
• Total length, couplings and restrictions
• Hole-to-string annular area
• Cuttings, water and depth

5. Correct for altitude, heat and engine capability

Lower inlet pressure at altitude changes compressor pressure ratio and can affect capacity, power and cooling; diesel engines also receive less oxygen. Atlas Copco advises considering ambient pressure, temperature, humidity, coolant temperature, compressor type and power source. Use the manufacturer's derating information instead of an improvised percentage. High temperature, dirty coolers or poor ventilation can limit sustained output, while cold conditions introduce starting, lubricant and condensate issues. Verify the worst expected environment and continuous operating point.

• Elevation or measured ambient pressure
• Temperature and humidity
• Engine and compressor derating
• Cooling and continuous-duty limits

6. Show secondary demand and contingency

List every device that may consume air simultaneously and decide whether it runs during drilling. Keep hammer demand, calculated line loss, auxiliary demand and contingency as separate entries rather than hiding uncertainty in one unexplained factor. More compressor is not automatically better: oversizing can add purchase cost, transport weight and fuel use, while undersizing can impair hammer operation and cleaning. Compare alternatives using expected cost or fuel per accepted metre under stated conditions, not hourly fuel alone or an unsupported production promise.

• Hammer demand
• Air-path losses
• Simultaneous auxiliary demand
• Documented contingency and cost assumption

7. Verify the actual used compressor

Photograph the compressor, airend and engine plates and reconcile them with the controller and listing. Record pressure, free-air delivery, power, hours and the date of each reading. Request service history for oil, filters, separator, valves, cooling and airend work; missing records remain unavailable, not assumed. Ask qualified personnel for a documented load test showing ambient conditions, selected pressure, stabilized duration, delivered output where measured, temperatures, warnings, smoke and leaks. An idle video does not prove compressor capacity, and a short test does not guarantee future reliability.

• Machine, engine and airend identity
• Service and repair history
• Documented load-test conditions
• Warnings, leaks and stabilized output

8. Produce a matching sheet before quotation

Name the rig, hammer, bit, rods, compressor, hose and site conditions on one sheet. Attach the hammer chart and compressor data used, and label each input as manufacturer data, observed unit evidence, buyer assumption or unresolved. Seek confirmation from the hammer maker, tool supplier or qualified drilling engineer before purchase. When contacting the dealer, send this duty sheet and stock ID so unit-specific data, additional tests and included equipment can be confirmed. This article does not confirm availability, performance or suitability of a current listing.

• One rig-hammer-compressor duty sheet
• Source and date for every value
• Open questions assigned for resolution
• Unit-specific confirmation before payment

9. Use a pressure-flow decision sheet for a listed compressor

For CR-004, the listing includes an XRHS836CD nameplate and a meter image, but the required pressure-flow pair and a current load-test record are not confirmed. Keep the sizing decision open until those data can be compared with the exact hammer chart. CR-025 has a separate model-identity conflict and cannot substitute its controller label for CR-004's data.

• An unresolved operating point means the compressor is a candidate for verification, not a confirmed match.

• Check XRHS836CD CR-004 and its nameplate
• Review the separate CR-025 identity conflict
• Compare used compressor listings

A nameplate example: Atlas Copco XRHS666 C · CR-057

CR-057 is listed as an Atlas Copco XRHS666 C. Its photographed nameplate records 18.6 m³/min @ 20 bar. This is a nameplate rating, not a current load-test result. Compare the exact hammer's air demand and site conditions, then confirm the used unit's tested output before selecting the package.

• Use stock ID CR-057 when requesting a load test for this machine.

• View XRHS666 C · CR-057
• Read the CR-057 machine nameplate